Motor vehicles are subject to limiting values, some of which are very strict, with respect to emissions of pollutants which are to be complied with. A precise fuel metering, inter alia, during injection is decisive in order to comply with present and, in particular, future emissions and exhaust gas limiting values.
In this case, it is to be taken into consideration, however, that different tolerances occur during the metering. Such metering tolerances generally result from specimen-dependent needle dynamics and specimen-dependent static flow rates of the fuel injectors. An influence of the needle dynamics may be reduced, for example, by way of a mechatronic approach, such as, for example, a so-called controlled valve operation. In a controlled valve operation, control times of the fuel injectors in the sense of a regulation are adapted, for example, throughout the service life of a motor vehicle. In this case, the control signal is detected during the injection and, in parallel thereto, the opening duration of the valve needle is ascertained from the opening and closing timing. Therefore, the actual opening duration of each injector may be calculated and, if necessary, corrected.
Such a method for regulating an actual opening duration of a valve to a setpoint opening duration is described in German Patent Application No. DE 10 2009 002 593 A1.
Possible errors in the static flow rate result from tolerances of the injection hole geometry and the needle lift. Such errors may so far usually only be corrected globally, i.e., jointly with respect to all fuel injectors of an internal combustion engine, for example on the basis of a lambda control or a mixture adaptation. As a result, it may not be detected, however, whether individual fuel injectors of the internal combustion engine have a deviation with respect to their static flow rate (i.e., they deliver different quantities during the same opening duration), which may be relevant in terms of exhaust gas or engine smoothness.
German Patent Application No. DE 10 2007 050 813 A1 describes, for example, a method for monitoring the delivery quantity of an injector control unit of an internal combustion engine, in which a fuel quantity delivered by the injector is monitored on the basis of a pressure drop in the high pressure accumulator. A detailed ascertainment of causes of possible deviations, and the correction thereof, is therefore not possible, however.
It is therefore desirable to provide a possibility for a more accurate monitoring and/or correction of a fuel metering in fuel injectors of internal combustion engines.